question regarding as3 flashvars

Hello guys! I just have a question on how to use a flashvars.

I know how to use it when using a timeline method but I can't see the value that i'm passing when using "class" method.

Here is my code.

package

{

          import flash.display.MovieClip;

          import flash.net.URLRequest;

          import flash.events.MouseEvent;

          public class powerade extends MovieClip

          {

                    public var face:mcFace;

                    public var test:mcTest;

                    public function powerade()

                    {

                              face=new mcFace();

                              addChild(face);

                              face.x=372.1;

                              face.y=246;

                              test=new mcTest();

                              addChild(test);

                              test.x=372.1;

                              test.y=450;

                              var flashvars1b=this.load.parameters;

                              var loader1b:Loader= new Loader();

                              loader1b.load(new URLRequest(flashvars1b.mainImage));

                              face.addChild(loader1b);

                    }

          }

}

it returns an error :

but when I tried to remove the code into red color, it works well.